This invention relates generally to amplifier circuits, and, more particularly, to wideband amplifier circuits that are specially configured to provide a high input impedance.
Wideband amplifier circuits are commonly used to amplify radio signals, including both am and fm broadcast signals, generated by a high impedance source such as an antenna. In the past, such amplifier circuits have frequently included reactive components specially tuned to the specific frequency bands desired, e.g., 540 to 1600 kHz for the am broadcast band and 88 to 108 MHz for the fm broadcast band. Such circuits have not proven to be entirely satisfactory when placed in mass production, however, because adjustments must ordinarily be made to the tuned circuits, thus adding to the labor costs.
Wideband amplifier circuits that don't include such tuned circuits are not believed to be in general use. This is possibly because non-tuned amplifier circuits were not previously available having an input impedance sufficiently high to amplify the am band signals, where the antenna impedance is relatively high, while at the same time having a sufficiently wide frequency response to also amplify the fm band signals.
It should therefore be appreciated that there is a need for an amplifier circuit having a relatively high input impedance at the am broadcast frequency band, while simultaneously having a frequency response extending at least to the fm broadcast frequency band. The present invention fulfills this need.